Hi Daniel,
that’s a common problem, but the thread Rollershutter with Homematic IP (HmIP) HmIPW-DRBL4 (german and external version from the same user here) gives you a workaround.
I’m very glad that @shuo figured that out for us. 
tl;dr: If you want to change the blades angle (just the angle, not the height), it will be triggered only if you send a 2nd command for changing the shutter height straight behind, even if the shutter height shall stay the same. Sounds weird, but that’s how it works. 
I dit it like this with my items:
Rollershutter Wintergarten_Jalousie_Tuer_Level2 <rollershutter> (gLamellen) ["Rollershutter"] {channel="homematic:HmIP-BBL:<your individual value here>:4#LEVEL_2"}
Switch Wintergarten_Jalousie_Tuer_Stop {channel="homematic:HmIP-BBL:<your individual value here>:4#STOP"}
Here are the 2 commands I’m speaking about taken from my rules, one after another:
Wintergarten_Jalousie_Tuer_Level2.sendCommand(50)
Wintergarten_Jalousie_Tuer_Stop.sendCommand(ON)
As you can see, I’m using a STOP command for my BBLs and not the 101% value as suggested in the link above, but there is no special reason I did it like this. Just do what fits you best.
The value 50 is just an example and will turn your blades horizontally.
For my complete rule you may want to take a look at Control HmIP rollershutter slates / blinds using groups in rules.