Yes, the key words are "They just sit there...". Similarly, another 88, or 188, or 288 tanks are in the same status (waiting mode, ready to quickly advance to the front line and open fire) on the governmental side. The same OSCE mission often reports that heavy weapons of the governmental forces disappeared from the locations they were supposed to be. No surprise, both sides do not trust each other and do not strictly follow fragile agreements like so-called "Minsk-2".
Thanks God, they all (tanks) are not shooting now. Only machine guns and light artillery sporadically "talk".
I find it stupid to say/write twice a sentence "pro-Russian", "Russian support" , etc. with regard to separatists. To be consistent, the other side should always be "marked" as "NATO backed" or "US controlled", but what's the use of escalating the tension? They all are (poor) Ukrainian citizens, involved in a civil war.
All possible means should be looked for and used to calm down the situation in that region.