Bizarre behavior when selecting a big compressed image

[lurch]

• Etcher version: 1.5.51 (x64 AppImage)
• Operating system and architecture: Ubuntu 16.04 x86
• Image flashed: see below...
• Do you see any meaningful error information in the DevTools?

/tmp/.mount_balenaBjVhdX/resources/app.asar/node_modules/raven-js/dist/raven.js:58 Download the React DevTools for a better development experience: https://fb.me/react-devtools
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/tmp/.mount_balenaBjVhdX/resources/app.asar/node_modules/raven-js/dist/raven.js:58  _____ _       _
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Version = 1.5.51, Type = appimage
/tmp/.mount_balenaBjVhdX/resources/app.asar/node_modules/raven-js/dist/raven.js:58 Tue Jul 02 2019 19:57:35 GMT+0100 (BST) Application start ({"packageType":"appimage","version":"1.5.51","applicationSessionUuid":"95db071a-6fdb-4c5c-b929-0b30508d19c9","sample":0.1})
/tmp/.mount_balenaBjVhdX/resources/app.asar/node_modules/raven-js/dist/raven.js:58 Tue Jul 02 2019 19:57:36 GMT+0100 (BST) SafeWebview loaded ({"event":{"fromCache":false,"headers":{"Accept":"text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8","Upgrade-Insecure-Requests":"1","User-Agent":"Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) balena-etcher-electron/1.5.51 Chrome/66.0.3359.181 Electron/3.1.9 Safari/537.36"},"id":11,"method":"GET","referrer":"","resourceType":"mainFrame","responseHeaders":{"Accept-Ranges":["bytes"],"Cache-Control":["public, max-age=0"],"Connection":["keep-alive"],"Content-Encoding":["gzip"],"Content-Type":["text/html; charset=UTF-8"],"Date":["Tue, 02 Jul 2019 18:57:36 GMT"],"Etag":["W/\"3a3d8-16bb2041748\""],"Last-Modified":["Tue, 02 Jul 2019 09:29:01 GMT"],"Server":["Cowboy"],"Transfer-Encoding":["chunked"],"Vary":["Accept-Encoding"],"Via":["1.1 vegur, 1.1 vegur"]},"statusCode":200,"statusLine":"HTTP/1.1 200 OK","timestamp":1562093856677.697,"url":"https://www.balena.io/etcher/success-banner/?etcher-version=1.5.51&api-version=2&optOutAnalytics=true"},"applicationSessionUuid":"95db071a-6fdb-4c5c-b929-0b30508d19c9","flashingWorkflowUuid":"94e0d1cd-3ec1-411c-8407-73f9486b75c5","sample":0.1})
/tmp/.mount_balenaBjVhdX/resources/app.asar/node_modules/raven-js/dist/raven.js:58 Tue Jul 02 2019 19:57:42 GMT+0100 (BST) Open image selector ({"applicationSessionUuid":"95db071a-6fdb-4c5c-b929-0b30508d19c9","flashingWorkflowUuid":"94e0d1cd-3ec1-411c-8407-73f9486b75c5","sample":0.1})
/tmp/.mount_balenaBjVhdX/resources/app.asar/node_modules/raven-js/dist/raven.js:58 Tue Jul 02 2019 19:57:58 GMT+0100 (BST) Open image selector ({"applicationSessionUuid":"95db071a-6fdb-4c5c-b929-0b30508d19c9","flashingWorkflowUuid":"94e0d1cd-3ec1-411c-8407-73f9486b75c5","sample":0.1})
/tmp/.mount_balenaBjVhdX/resources/app.asar/node_modules/raven-js/dist/raven.js:58 Tue Jul 02 2019 19:58:03 GMT+0100 (BST) Select image ({"image":{"size":1866465280,"compressedSize":368428079,"logo":false,"name":"2018-11-13-raspbian-stretch-lite.img","hasMBR":true,"partitions":[{"offset":4194304,"size":46005248,"type":12,"index":1},{"offset":50331648,"size":1816133632,"type":131,"index":2}],"path":"/home/qpc/Downloads/2018-11-13-raspbian-stretch-lite.zip","extension":"zip","blockMap":false},"applicationSessionUuid":"95db071a-6fdb-4c5c-b929-0b30508d19c9","flashingWorkflowUuid":"94e0d1cd-3ec1-411c-8407-73f9486b75c5","sample":0.1})
/tmp/.mount_balenaBjVhdX/resources/app.asar/node_modules/raven-js/dist/raven.js:58 Tue Jul 02 2019 19:58:49 GMT+0100 (BST) Select image ({"image":{"name":"uSD_C5.img","size":63864569856,"compressedSize":9292804,"isSizeEstimated":false,"hasMBR":true,"partitions":[{"offset":16777216,"size":63847792640,"type":7,"index":1}],"path":"/home/qpc/SD_card_images/uSD_C5.img.xz","extension":"xz","logo":false,"blockMap":false},"applicationSessionUuid":"95db071a-6fdb-4c5c-b929-0b30508d19c9","flashingWorkflowUuid":"94e0d1cd-3ec1-411c-8407-73f9486b75c5","sample":0.1})

I just saw some very strange behaviour in Etcher - at first I thought it was a fluke, but then found out it's reproducible...
In the procedure below, uSD_C5.img.xz is an image file I made of a 'fresh' (i.e. empty) 64GB micro SD card which I've compressed with xz, and 2018-11-13-raspbian-stretch-lite.zip is an (older) image from raspberrypi.org

1. Open up Etcher 1.5.51
2. Select the uSD_C5.img.xz image
3. Etcher doesn't appear to have done anything... the left-most button still says "Select image"
4. Select the 2018-11-13-raspbian-stretch-lite.zip image
5. The Etcher GUI updates to say that the stretch-lite image has been selected
6. Wait a while...
7. The Etcher GUI spontaneously updates to say that the uSD_C5 image has been selected! 😕 Which "overrides" the stretch-lite image that I selected in the mean-time.

Looks like Etcher must be decompressing the xz-compressed image in the background, and then the GUI spontaneously updates once it's finished decompressing? Possibly related to #2770 ?