Suddenly cannot select multiple sheets in Calc

Using LibO 6.0.7.3 Calc in Ubuntu 18.04 I am unable to select multiple sheets.
In previous versions I could always do this by holding Ctrl or Shift whilst selecting tabs.
I can still do this OK in LibO 5.1.6.2 which I have on another partition.
Is this a bug or ???

PS I just found that multiple sheets ARE selected, but the tabs don’t show that…

PPS To fix this, I had to “Select all sheets” then “Tab color” then select any color other than “Default”.
After that, selected tabs appear white & other tabs appear colored, so you can see which are selected.
Seems like a bug to me…

PPPS I had already searched for bugs without finding, but I have since found at least 2:
https://bugs.documentfoundation.org/show_bug.cgi?id=104564

https://bugs.documentfoundation.org/show_bug.cgi?id=88840

So it is a real problem & a real bug, but no solution…

I think it’s not a bug, but a bad choice of a hard coded colour.

For me (underWin 10) the difference in tab colour between a selected and an unselected sheet exists, but is minimal. I only can notice it when changing the selection state. The selected tab shows (about?) the lightest shade of gray from the standard palette while the default tab colour for unselected sheets seems to be white…