'Open image in new tab' discrepancies

[a10]

2.1.4, w8.1, FF 140.0.1, not tested any other browser.

'Open image in new tab' from inserted image (within text) > downloads the image to pc and shows a blank FF tab.
with url: forum/index.php?action=dlattach;attach=59596

'Open image in new tab' after opening attached image from thumbnail (bottom of post) > opens image in new tab.
with url: index.php?action=dlattach;attach=59598;image

Edit:
Tested w10, latest Vivaldi, same regarding inserted image, goes to downlad instead of oepning in new tab (Vivaldi shows a download popup menu).

Edit 2: regarding inserted images, want thumbnails, no large pics or full size. Did I miss some setting that forces thumbnails within text (to behave exactly like under-post thumbnails) ?

[Sir Osis of Liver]

Same in 2.1.3, FF110.