Downloaded and installed 220.127.116.11.
A "Displayed as":
1 1 1/8 (1.125) all is good
2 1 ¼ (1 1/4) all is not so good
3 1 1/8
4 1 ¼
Operating System: Windows 7
Version: 18.104.22.168 release
What you just described is not a bug.
Since no 'fraction' format was set first for those cells, the result you described is as expected.
If you first format the cells as fraction before inserting the data, then they are shown as fractions (not with decimals), except for your "1 1/4", which is still interpreted as text.
I would agree that "1 1/4" should remain as 'fraction' when the cell has already been formatted as 'fraction'. You already reported such behavior in bug #71974.
Since the initial format you describe in this report is different from what you describe in bug #71974, this is not exactly a duplicate.
Since the behavior described here is as expected, I am closing this report as NOTABUG.
If you have something to add regarding this issue, please do it in bug #71974
at https://bugs.freedesktop.org/show_bug.cgi?id=71974 where you can log-in too.