Leinster's third defeat in six Magners League games left coach Michael Cheika frustrated by the province's current lack of consistency.
Brian O'Driscoll and company were gunning for their third successive win in the league on Friday night but they were foiled by the Borders in a 22-19 defeat.
Leinster nudged 19-13 ahead after the interval and looked to be on course to repeat their brace of wins over the Scots last season, but Steve Bates' hosts were strongest in the final 20 minutes - full-back Calum MacRae dinked over two penalties and young out-half Steve Jones booted a late drop goal to ruin Leinster's visit to a misty Netherdale.
Cheika said: "It'd be disrespectful to the Borders if I said we lost the game. We were in a position to win the game, but we had moments where we didn't play very smart football."
Worryingly, just a week ahead of their Heineken Cup opener at home to Gloucester, scrum half Guy Easterby, who is set to be out for six to eight weeks with a broken jaw, winger Denis Hickie (lower back) and flanker Cameron Jowitt (shoulder) were all in the wars.
Cheika will monitor the progress of the latter two over the next few days, as well as trying to take the positives from the Borders' match video,
He added: "The first half (against the Borders) was alright. They came out steaming and we hung in there even though we didn't play too well and sometimes you've got to do that.
"In the second half we showed a lack of control and a lack of maturity to finish the game off. It's not something that we can afford to do. We're trying to make ourselves more consistent and we took a step backwards."
Meanwhile with the focus on Europe for the next two weekends, Leinster skipper O'Driscoll is keen for his men to go one better than last season when they faltered in the final four.
The Ireland and Lions centre said: "Seeing what Munster did last year is a big incentive. We were massively envious of their success and achievement, and we want to emulate it.
"It's going to be a very competitive and open Heineken Cup again. It certainly won't be just the English and French sides fighting it out for the trophy."