diff --git a/src/qt/bitcoinunits.cpp b/src/qt/bitcoinunits.cpp
index 64751c178..21aed235c 100644
--- a/src/qt/bitcoinunits.cpp
+++ b/src/qt/bitcoinunits.cpp
@@ -148,6 +148,21 @@ QString BitcoinUnits::format(int unit, qint64 n, bool fPlus, SeparatorStyle sepa
 }
 
 
+// TODO: Review all remaining calls to BitcoinUnits::formatWithUnit to
+// TODO: determine whether the output is used in a plain text context
+// TODO: or an HTML context (and replace with
+// TODO: BtcoinUnits::formatHtmlWithUnit in the latter case). Hopefully
+// TODO: there aren't instances where the result could be used in
+// TODO: either context.
+
+// NOTE: Using formatWithUnit in an HTML context risks wrapping
+// quantities at the thousands separator. More subtly, it also results
+// in a standard space rather than a thin space, due to a bug in Qt's
+// XML whitespace canonicalisation
+//
+// Please take care to use formatHtmlWithUnit instead, when
+// appropriate.
+
 QString BitcoinUnits::formatWithUnit(int unit, qint64 amount, bool plussign, SeparatorStyle separators)
 {
     return format(unit, amount, plussign, separators) + QString(" ") + name(unit);