I had an Syn standing of above 49% already and gained their researched techs. Then i have “borrowed” a Tiamat from Syn. After this i did several standing improving action like raiding New Jericho. But the standing is capped out at 49% and does not further increase now.
You need to do one of their faction specific missions (eg third initiation etc).
But he already did it, so it won’t show again.
Is it intended, if you was already at over 49% standing and you fall below 50% standing, you are supposed not go above 49% once again?
that is a bug, it doesn’t work that way.
If you unlock REP 49+ , diplomacy mission, and then you lose REP, you will have lower that 49,
but there are not limitations, you should be able to gain REP without restrictions until REP 74
Yes it is a bug. F12 Report…
Are you sure about that ? 
Sorry, Helios. My mistake 